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Old 07-26-2015, 03:03 PM   #1
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Weighed RV, how do I use this data to determine tire pressure?

After 4 years of ownership, I finally had my 2004 Fleetwood Fiesta 32S (Ford V10) weighed after installing 6 new tires. I used one of the CAT scales, which I know is not the most desirable, since they only do individual axle weights, as opposed to individual wheels. I still felt that was better than nothing at all. I had just filled up with fuel, and had a full load of water on board, the scale was empty, so I decided to go for it.

What I am unclear on is how to use this information, along with the tire manufacturer's dimension data sheet, and the wall placard on the RV, to determine what to set my tire pressures at. I read all of the most recent threads related to weight, tires and tire inflation, but still need some help with this.

Anyway, the tires are Hankook AH11, size 245/70R19.5. Their data sheet lists the max. pressure at 110 psi. Max load is listed at 4940 single and 4675 dual.

The placard inside the RV lists a GVWR of 20,500, a front GVWR of 700, and a rear of 13,500. It also lists an inflation of 80 psi.

The CAT scale shows a steer axle weight of 5,560 lbs, and a drive axle weight of 10,980, for a total gross weight of 16,540. I just completed a 3868 mile trip, and ran the tires at 90 psi. They were all a touch over 100 psi at the end of a day's driving.

Doing the math, it seems I have enough tire to support the vehicle. I don't understand the front GVWR of 700 lbs. Surely the V10 alone weighs more than that, so I'm sure that I am missing the boat on something.

Thanks in advance for any suggestions!
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Old 07-26-2015, 03:12 PM   #2
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FWIW, even though the CAT website says that they only do axle weights, I asked and was given permission by the site manager to straddle the side of the scale for four-corner weights. Not all sites will work for this, though. The scale needs to be reasonably level with the surrounding pavement. You can do three passes over the scale and use the individual corner weights to determine what percentage of the axle weight that each is carrying. The truckers will probably think you're crazy.



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Old 07-26-2015, 03:24 PM   #3
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Originally Posted by terryl View Post
Anyway, the tires are Hankook AH11, size 245/70R19.5. Their data sheet lists the max. pressure at 110 psi. Max load is listed at 4940 single and 4675 dual.

The placard inside the RV lists a GVWR of 20,500, a front GVWR of 700, and a rear of 13,500. It also lists an inflation of 80 psi.

The CAT scale shows a steer axle weight of 5,560 lbs, and a drive axle weight of 10,980, for a total gross weight of 16,540. I just completed a 3868 mile trip, and ran the tires at 90 psi. They were all a touch over 100 psi at the end of a day's driving.

Doing the math, it seems I have enough tire to support the vehicle. I don't understand the front GVWR of 700 lbs. Surely the V10 alone weighs more than that, so I'm sure that I am missing the boat on something.

Thanks in advance for any suggestions!
Sounds like the front GAWR (gross axle weight rating) should probably be 7000lbs. The total GVWR is the combination of the rear GAWR and front GAWR. 7000 + 13500 = 20500.

So you have 1440lbs of cargo capacity on the front axle, and 4020lbs of capacity on the rear.

The pressure list on the tire means you should not run the tire over that amount, cold.
The pressure list on the RV VIN tag is just from the mfg, and doesn't really count for much.

I don't have it but I'm sure someone can find it: there will be a chart somewhere from Hankook that says if the tire has this much weight on it, the pressure should be this much.

So for the front, each tire weighs (roughly) 2780lbs.
Each tire on the rear weighs (roughly) 2745lbs each.
Of course, those numbers will change depending on what you put in/take out of the MH.
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Old 07-26-2015, 07:12 PM   #4
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Originally Posted by terryl View Post
After 4 years of ownership, I finally had my 2004 Fleetwood Fiesta 32S (Ford V10) weighed after installing 6 new tires. I used one of the CAT scales, which I know is not the most desirable, since they only do individual axle weights, as opposed to individual wheels. I still felt that was better than nothing at all. I had just filled up with fuel, and had a full load of water on board, the scale was empty, so I decided to go for it.

What I am unclear on is how to use this information, along with the tire manufacturer's dimension data sheet, and the wall placard on the RV, to determine what to set my tire pressures at. I read all of the most recent threads related to weight, tires and tire inflation, but still need some help with this.

Anyway, the tires are Hankook AH11, size 245/70R19.5. Their data sheet lists the max. pressure at 110 psi. Max load is listed at 4940 single and 4675 dual.

The placard inside the RV lists a GVWR of 20,500, a front GVWR of 700, and a rear of 13,500. It also lists an inflation of 80 psi.

The CAT scale shows a steer axle weight of 5,560 lbs, and a drive axle weight of 10,980, for a total gross weight of 16,540. I just completed a 3868 mile trip, and ran the tires at 90 psi. They were all a touch over 100 psi at the end of a day's driving.

Doing the math, it seems I have enough tire to support the vehicle. I don't understand the front GVWR of 700 lbs. Surely the V10 alone weighs more than that, so I'm sure that I am missing the boat on something.

Thanks in advance for any suggestions!
According to the Hankook inflation tables your front tires @ 80PSI can support 3640lbs per tire, and the rear can support 3415lbs each. So it looks like @ 80 PSI you have plenty of load carrying capacity and safety margin in your tires.
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Old 07-26-2015, 07:44 PM   #5
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Thanks to both of you for this very useful information. I thought the ride was pretty comfortable at 90 psi, but it will be nice to drop it another 10 lbs on the next big trip (next month) to see if it smooths things out even more.

jesilvas, it never occurred to me that the 700 lb front GVWR listed on both the driver's area placard, as well as the one in the wardrobe closet was a misprint, so I never did the calculation that you pointed out to me. But it all makes sense now, that someone at the Fleetwood plant left off a zero (twice)!

lllkrob, do you have a link to where I can find and print out a copy of the Hankook inflation tables? I spent quite a bit of time on their website yesterday, and wasn't able to find anything other than size, max. air pressures and max. loads.

Thanks again, guys!
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Old 07-26-2015, 07:56 PM   #6
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Just a note: NEVER adjust your tire pressure just after coming off the road or with the tires in the sunshine. Tires are built with the foreknowledge of the pressure going up as they get warmed by driving. Heating the tires in the sun reduces the accuracy of what you are actually charging them to.
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Old 07-26-2015, 10:01 PM   #7
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Never run less than what is listed on the tire placard, that is what Michelin, Goodyear, Firestone, etc advise. That is the position of the RMA=Rubber Manufacturers Association, as ch 4 of their pdf also states.
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Old 07-26-2015, 10:35 PM   #8
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Never run less than what is listed on the tire placard, that is what Michelin, Goodyear, Firestone, etc advise. That is the position of the RMA=Rubber Manufacturers Association, as ch 4 of their pdf also states.
That document appears to be for passenger tires and light truck tires and sizes 15 or 16 inch.
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Old 07-26-2015, 10:45 PM   #9
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maybe this one.
[IMG]1994brave29rqrv.blogspot.co[/IMG]
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Old 07-26-2015, 11:56 PM   #10
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Thanks, Dan. That chart back up the numbers that lllkrob provided earlier. I will save that info in the event that my gross weight changes in the future.
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Old 07-27-2015, 09:33 AM   #11
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This video by Michelin explains a lot about tire care, including how to determine correct pressure.

https://www.youtube.com/watch?featur...&v=Wb7W-nRAPrk
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Old 07-27-2015, 09:59 AM   #12
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I would be very cautious about what PSI you run with. As you were not able to get a 'four corner weight', it's very possible that one axle of either front or rear, could have a much higher weight on it then the other. (Our 98 T28 Bounder, when fully loaded, including water and full tank of gas, was much heavier on the back right side then the left. (Can't remember now, but it was significant.)

Going to a moving company, or a place that charges waste disposal by the bound, and then repeating the weights with the 'straddle' technique, stopping to get first the front axle, before moving on to get the rear, so you can do the math from the non straddle axle weights, is the only way to get four corners. (Unless you go a place that has the individual scales for each axle.)

I then also 'round up' if I'm say within 25% of the of the range of weights, I move up to the next line. I also then take that Tire Manufactures PSI, and add an additional 5 PSI on top of it. These two steps give you a safety margin for adding extra weight, as well as handling the extra weights that say a prolong side wind can load onto a tire. As well as a little forgiveness while traveling for gradual loss of PSI.

And, I personally do follow the Tire Manufacturers PSI for Weight chart info, over the placard that comes in the RV. In my case, with rounding up, and the extra 5 PSI, I'm still running between 10 to 15 PSI below the max all around weight of 120 PSI of the placard. I feel safe, and also have a much more forgiving ride, especial where the front end works into ride comfort.

But each of us must do what we feel is right for us, and make our own decisions.

IMO, if you do not get four corner weight. Assume an out of balance condition exists on your coach, especially on the drive wheels, and add 750 lbs to your rear individual rear calculations. And probably 400 lbs to your front. And use those values when going to the Tire Manufacture PSI recommendations. And still do the rounding up if within 25%, and extra 5 PSI. (BUT, STILL RECOMMEND ACTUAL FOUR CORNER WEIGHT ACTUALS!)

You might also go to the owners group of your coach, and ask if others would share their four corner weight info. Look for the difference between axle side by side weights, and see if they get you closer to my suggested values above.

And salute to getting this info, sure been a few years - but for sure no time like the present to get the best PSI for your coach. Tire safety is so often overlooked, and it really is a key difference maker on the safety for you as you travel. (And others, as blowouts can impact others too!

Best of luck to you,
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Old 07-27-2015, 10:13 AM   #13
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Never run less than what is listed on the tire placard, that is what Michelin, Goodyear, Firestone, etc advise. That is the position of the RMA=Rubber Manufacturers Association, as ch 4 of their pdf also states.
Ray, this topic is a hot repeat, as you know.

For the trucking or commercial industry you are correct. The load weight is often at what the unit is designed for. This is different for RV's.

The place card rating is for loading the chassis to the max of what it is designed for. Running the tires at the pressure they are designed for for the weight they are carrying after a 4 point scale weighing is not a bad thing to do. The important thing here is to keep your load constant and use the cold psi recommendation from the manufactures table. The correct setting is by using the heaviest tire position on the axle as the point of reference on the chart.

One trucker, now RVer, recommended adding a pound to the crown pull side of your front tires. I went to a Blue Ox TruCenter to correct that. Love it.

Back to the tires. Like any tire that is over or under inflated for the average load it will carry, it will wear poorly.

I strongly recommend a TPMS. These things are only a warning devise and should never be relied upon as a calibrated test instrument. Before you start to roll you have a visual benchmark of the internal condition of your tires. If one suddenly deviates from the trend change of the other tires you can bet that one is about to fail or has already.

Tire pressure is a relative variable at best that we try to keep at a safe reference point before we start our days travels. Start of day ambient temperature is so all over the board. One morning the tires could be at 55* at the beginning of your drive, 95* at the end of your drive and 75* the next morning before you hit the road. We must be diligent in monitoring our tire pressure before each days drive.

Here is an example of how drastically the tire pressure can change from morning to morning: I could start my drive from San Diego, CA on morning and it is 85*, so I set my tires to 110psi as I am supposed to. My days drive takes me into the mountains. The next morning it is 55* out. My tire pressure could have dropped by 6 psi or more, depending on how much humidity is in the air within the tires. (I recently added a air dryer and filter to my pancake compressor.) If I were to start the day without correcting the cold psi I would be running on under inflated tires.

Well, being diligent, I corrected my tire pressure when in the mountains and before my days travels but the next morning I wake up in the desert. I get a late start and now the temperature out side is 95*. My tires could now be 10 or more psi overinflated. And the sun is shinning on them..

There is no easy way to keep your tires perfectly inflated. Diligence is the only way and hope that the design specs of the tires will keep us safe when we error for one reason or another.

Happy trails all,
Rick Y
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Old 07-27-2015, 10:15 AM   #14
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Originally Posted by wigginsjsr View Post
This video by Michelin explains a lot about tire care, including how to determine correct pressure.

https://www.youtube.com/watch?featur...&v=Wb7W-nRAPrk
Good info thanks.
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